# Thread: what is causing the Moon to move away from Earth?

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Is outwards travel of Deimos also observed?

Unlike Earth, Mars is a desert planet with no shallow oceans to dissipate tides, and only thin air. How much is Mars able to accelerate Phobos or Deimos, compared to Earth?

2. Originally Posted by chornedsnorkack
Is outwards travel of Deimos also observed?

Unlike Earth, Mars is a desert planet with no shallow oceans to dissipate tides, and only thin air. How much is Mars able to accelerate Phobos or Deimos, compared to Earth?
I expect it to be less than it would be with continents and oceans like those on Earth.

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Originally Posted by grant hutchison
It's an observed effect, and it can be shown mathematically, with calculations matching observation.
If the tidal bulge raised by a moon is always ahead of it in its orbit (as it is when the parent planet rotates faster than than the moon orbits), then the tidal evolution is outwards.
If the tidal bulge raised by a moon is always behind it in its orbit (as it is when the moon orbits faster than the planet rotates, or in the opposite direction to planet rotation), then the tidal evolution is inwards.

All the bodies in my list are moving around their parent planets faster than the planet rotates, so all wil evolve inwards tidally.

Grant Hutchison
Thanks

However, if I understand it correctly -
Currently we have ONLY measured the drifting direction of the moon from Earth and Earth from the Sun.
In both cases we have found the orbital moon/planet is drifting outwards.
Did we set any real measurements for other orbital moon or planet?
If no, then technically we can say that 100% of the orbital moon or planet which have measured are drifting outwards!
Therefore, why can't we just assume that all orbital moon/planet are drifting outwards regardsless of the planet rotation?

With regards to the following cases:
"when the moon orbits faster than the planet rotates, or in the opposite direction to planet rotation"
Why can't we say that it is just a hypothesis idea as we don't have a real mesurement prove for that?

What is the chance that Triton is also drifting outwards?
Last edited by Dave Lee; 2018-Jan-04 at 02:53 PM.

4. Originally Posted by Dave Lee
<snip>
If no, then technically we can say that 100% of the orbital moon or planet which have measured are drifting outwards!
Therefore, why can't we just assume that all orbital moon/planet are drifting outwards regardsless of the planet rotation?
Because we have a mechanism that explains the changes we observe and your assumption would violate that physics. You would need data showing the physical explanation we have is wrong and new mechanism to explain this.

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Originally Posted by Hornblower
I expect it to be less than it would be with continents and oceans like those on Earth.
Yes, but have we actually measured how much less?

Also: is Nyx drifting due to tides? If yes, in which direction?

6. Originally Posted by Dave Lee
Thanks

However, if I understand it correctly -
Currently we have ONLY measured the drifting direction of the moon from Earth and Earth from the Sun.
In both cases we have found the orbital moon/planet is drifting outwards.
Did we set any real measurements for other orbital moon or planet?
Yes, we have measured the inward migration of Phobos, as I have already mentioned. Observation matches theory, and observation doesn't match whatever idea it is you have.

Grant Hutchison

7. Originally Posted by chornedsnorkack
Unlike Earth, Mars is a desert planet with no shallow oceans to dissipate tides, and only thin air. How much is Mars able to accelerate Phobos or Deimos, compared to Earth?
The time constant of migration is inversely proportional to the tidal dissipation factor, Q. Murray & Dermott give values of Q for Earth = 12 and Mars = 86, and suggest that 100 is a good general working figure for rocky or icy bodies. Of course, other things like mass ratios and orbital radii are important, too. You could look up the relevant equations if you want to know more.

Grant Hutchison

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Originally Posted by grant hutchison
The time constant of migration is inversely proportional to the tidal dissipation factor, Q. Murray & Dermott give values of Q for Earth = 12 and Mars = 86, and suggest that 100 is a good general working figure for rocky or icy bodies. Of course, other things like mass ratios and orbital radii are important, too. You could look up the relevant equations if you want to know more.
Or derive them. They are fairly simple, except for the precise definition of Q.
The tidal bulges raised in Mars by Phobos and Deimos travel in opposite directions through each other.
Do observed inward migration of Phobos and outward migration of Deimos give equal Q value for Mars, being inherent property of Mars irrespective of the amplitude and frequency of the tides?
Which bodies, if any, besides Earth and Mars possess directly observed Q?

9. Originally Posted by chornedsnorkack
Which bodies, if any, besides Earth and Mars possess directly observed Q?
Quantification of tidal parameters from solar system data (2016).
Note that Q is used to designate the "tidal quality factor" in this paper.

Grant Hutchison

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Originally Posted by grant hutchison
Yes, we have measured the inward migration of Phobos, as I have already mentioned. Observation matches theory, and observation doesn't match whatever idea it is you have.

Grant Hutchison
Phobos -
We call it moon, but it is irregularly shaped object with a mean radius of only 11 km:
https://en.wikipedia.org/wiki/Phobos_(moon)
"Phobos is a small, irregularly shaped object with a mean radius of 11 km (7 mi)"

Did we try to measure at least one moon with sphere shaped and some minimal size (as our moon) from the following list:

Originally Posted by grant hutchison

JUPITER
Metis

URANUS
Juliet
Portia
Rosalind
Cupid
Belinda
Perdita

NEPTUNE
Thalassa
Despina
Galatea
Larissa
Last edited by Dave Lee; 2018-Jan-04 at 06:29 PM.

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Originally Posted by Dave Lee
Did we try to measure at least one moon with sphere shaped and some minimal size (as our moon) from the following list:
The Moon is the 14th largest object in the solar system. It is larger than all of those satellites listed. Ergo your question is not possible to answer as none of the listed objects meet your arbitrary criteria.

12. Originally Posted by Dave Lee
Phobos -
We call it moon, but it is irregularly shaped object with a mean radius of only 11 km:
https://en.wikipedia.org/wiki/Phobos_(moon)
"Phobos is a small, irregularly shaped object with a mean radius of 11 km (7 mi)"
Yes. It's also dark brown in colour. Both facts are irrelevant.

Grant Hutchison

13. Originally Posted by Dave Lee
Same issue with phobos, which looks like a big rock.
Aren't all moons just big rocks?

14. Originally Posted by Dave Lee
Did we try to measure at least one moon with sphere shaped and some minimal size (as our moon) from the following list:
They (the list) all are likely measured and can be found on Wiki. Moons that are more than about 450km in radius will likely be considered round, as would serve to meet the "dwarf planet" status for non-satellites. Ceres may be the smallest dwarf planet at ~ 473km, but it does have some irregularity in dimensions, but so does Earth, well, and me too for that matter.

Here is a graphical list of planets and moons that will reveal the round ones. Look for Ceres (red bar) as a marker near the boundary of "roundness".
Last edited by George; 2018-Jan-04 at 10:49 PM.

15. And incidentally, Pluto and Charon are mutually tidally locked, so they remain at the same distance, correct?

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Originally Posted by George
Ceres may be the smallest dwarf planet at ~ 473km, but it does have some irregularity in dimensions, but so does Earth, well, and me too for that matter.

Here is a graphical list of planets and moons that will reveal the round ones. Look for Ceres (red bar) as a marker near the boundary of "roundness".
Thanks

Let's focus only on round moons as stated in the following list:

https://en.wikipedia.org/wiki/List_o...bjects_by_size

The size is less important. However, let's look on moons with minimal radius of 200 Km.

For example - Miranda, which is the moon of Uranus. (However, we can't use it for our case)

Originally Posted by Jens
And incidentally, Pluto and Charon are mutually tidally locked, so they remain at the same distance, correct?
This is very interesting issue. It is a good study case.
Both objects are considered as round shaped.
We must get real measurements and compare it to our hypothesis
Last edited by Dave Lee; 2018-Jan-05 at 06:30 AM.

17. Originally Posted by Dave Lee
Let's focus only on round moons as stated in the following list:
What is the significance of them being round or not?

We must get real measurements and compare it to our hypothesis
What hypothesis?

18. Originally Posted by Jens
And incidentally, Pluto and Charon are mutually tidally locked, so they remain at the same distance, correct?
well binary neutron stars spiral inwards because of gravitational waves, but I don't know.

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Originally Posted by Strange
What is the significance of them being round or not?
It is very, very important!
There is only one way to create round star, planet or moon.
However, I would prefer to avoid the discussion on this issue at this tread.
So please, let's just focus on round moons.

20. Originally Posted by Dave Lee
The size is less important. However, let's look on moons with minimal radius of 200 Km.
Many that small are surprisingly spherical. Enceladus and Mimas are just two examples, though surface structures can be very dramatic.

For example - Miranda, which is the moon of Uranus. (However, we can't use it for our case)
Also known as "Frankenstein" due to surface features.

21. Originally Posted by chornedsnorkack
Is outwards travel of Deimos also observed?

Unlike Earth, Mars is a desert planet with no shallow oceans to dissipate tides, and only thin air. How much is Mars able to accelerate Phobos or Deimos, compared to Earth?
There is also internal damping of the materials constituting the interior of the planet. You can demonstrate this sort of dissipation mechanism by repeatedly and rapidly flexing a small paperclip and touching it to your upper lip; you will note that the paper clip is warm. You can also get this same effect if you rapidly bend a piece of wire.

Because of Mars' internal structure, which I believe has no molten core, it may have lower internal damping than Earth. I don't know, offhand, the relative contribution of the oceans and other surface water to dissipating tidal energy vs the planetary interior.

22. Originally Posted by Dave Lee
It is very, very important!
There is only one way to create round star, planet or moon.
What is that? And how is it different from how non-round moons are created?

However, I would prefer to avoid the discussion on this issue at this tread.
So please, let's just focus on round moons.
I think that if it is so important, you should explain why.

23. Originally Posted by Strange
I think that if it is so important, you should explain why.
Yet not if it will diminish the impact he wants to have with his ideas for some future SF publication, which I think is the reason. [I think he did mention this somewhere but I can't seem to find it off-hand.]

24. Originally Posted by George
Yet not if it will diminish the impact he wants to have with his ideas for some future SF publication, which I think is the reason. [I think he did mention this somewhere but I can't seem to find it off-hand.]
Trying to rewrite the theory of tidal evolution to fit a science fiction plot device seems a little extreme though, doesn't it?
I'm with Strange - trying to answer questions satisfactorily when the questioner has an undisclosed agenda is frustrating for all concerned.

Grant Hutchison

25. Originally Posted by grant hutchison
Trying to rewrite the theory of tidal evolution to fit a science fiction plot device seems a little extreme though, doesn't it?
I'm with Strange - trying to answer questions satisfactorily when the questioner has an undisclosed agenda is frustrating for all concerned.
I think he just wants to keep secret his plot that seems to require a round moon. I recall one prominent author excited about a book idea and then shared the idea with friends, but the impetus was gone and the book never got writ.

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Originally Posted by Strange
What is that? And how is it different from how non-round moons are created?
I think that if it is so important, you should explain why.
Let me just say that none round moons are broken moons, or left over from a collision.
Therefore, those broken moons might migrate inwards.

27. Originally Posted by Dave Lee
Let me just say that none round moons are broken moons, or left over from a collision.
Not necessarily. Look at comet 67P and there is significant evidence that they joined together at an early date. These objects can get captured by planets or smaller objects.

Therefore, those broken moons might migrate inwards.
The tidal stress would be greater depending on orientation and they would break easier.

28. There's no reason a round moon couldn't previously have been broken into pieces by a collision, and then reassembled. For a time, that's we thought had happened to Uranus's moon Miranda.

Grant Hutchison

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Originally Posted by grant hutchison
There's no reason a round moon couldn't previously have been broken into pieces by a collision, and then reassembled. For a time, that's we thought had happened to Uranus's moon Miranda.

Grant Hutchison
Let me use the following question:

How do you set a round bread.

Normally it is expected to set it in the oven.
However, after you have it, cut it to many many pieces.
Now, can you reassemble those pieces into the same nice round bread?

In the same token.
If you wish to have a round moon - you have to use a very unique oven of the nature.
If later on, you cut it to pieces and reassemble it - it will look like a reassemble round bread...
You will get a broken moon.

30. Originally Posted by Dave Lee
Let me use the following question:

How do you set a round bread.

Normally it is expected to set it in the oven.
However, after you have it, cut it to many many pieces.
Now, can you reassemble those pieces into the same nice round bread?

In the same token.
If you wish to have a round moon - you have to use a very unique oven of the nature.
If later on, you cut it to pieces and reassemble it - it will look like a reassemble round bread...
You will get a broken moon.
None of which has anything to do with whether it migrates in or out from tidal interaction with its planet.

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